This application relates to the separation of helium-3 (hereinafter, “He-3”) from helium.
He-3 and helium-4 (hereinafter “He-4”) are naturally-occurring isotopes of helium. He-3 is currently used in a variety of applications, including neutron detection instruments, cryogenics, medical imaging, and nuclear fusion research. The He-3 concentration in naturally-occurring helium (hereinafter, “helium”) is very small—typically on the order of 0.1-1.0 ppm by volume, with the remainder comprising He-4.
In 1995, Kuz'menko and Lebedev (1995, Kuz'menko and Lebedev, Chemical and Petroleum Engineering, Vol. 31, Nos. 1-2, 1995, translated from Khimischeskoe I Neftyanoe Machinostroenie, No. 2, pp. 38-39, Feb. 1995) demonstrated that it is possible to separate He-3 from helium under laboratory conditions, using a conventional distillation process in a laboratory-sized packed column. The column used in this study was very small, having a column diameter of 20 mm and height of 200 mm.
Commercial-scale production of He-3 is impractical, however, using distillation processes of the prior art. Typical purity requirements for He-3 are in the range of 99.9% to 99.9999%. Due to the very low concentration of He-3 in naturally-occurring helium, it could take several months, or even years, for the He-3 concentration in the top of a conventional distillation column to reach an acceptable level, particularly if the desired He-3 purity is high, such as 99.9% or higher.
Therefore, there is a need for an improved distillation process that is suitable for commercial-scale recovery of He-3.